1. Technology Field
The present invention relates to a data storing method. More particularly, the present invention relates to a data storing method for a rewritable non-volatile memory module, a memory control circuit unit, and a memory storage apparatus using the same.
2. Description of Related Art
Along with the widespread of digital cameras, cell phones, and MP3 in recently years, the consumers' demand for storage media has increased drastically. Since a rewritable non-volatile memory has the characteristics of non-volatility of data, low power consumption, small volume, non-mechanical structure, and fast reading and writing speed, the rewritable non-volatile memory is the most adaptable memory to be applied in a portable electronic product, e.g., a notebook computer. A solid state drive (SSD) is a storage apparatus which utilizes a flash memory as its storage medium. Therefore, the flash memory industry has become a very popular part of the electronic industry in recent years.
Additionally, a NAND flash memory may be classified into a Single Level Cell (SLC) NAND flash memory, a Multi Level Cell (MLC) NAND flash memory or a Trinary Level Cell (TLC) NAND flash memory.
However, no matter what flash memory module, when multiple reading operations are performed on the flash memory module, for example, with a hundred thousand to a million reading times, there would be a possibility that error bits occur at the read data, and more even, the data stored in a physical erasing unit, which is already read for several times, would be lost or have an abnormal states. This phenomenon is referred as the read-disturb by the person skilled in the art. Especially, the flash memory module stores the system data of the flash memory storage system (e.g., The Firmware Code, The File Allocation Table (FAT)), and the system data will be read very frequently during the operation period of the flash memory storage system.
FIG. 1 is a diagram of the flash memory unit according to the related art.
Referring to FIG. 1, a flash memory unit 1 includes a charge-trapping layer 2 for storing electrons, a control gate 3 for applying a voltage, a tunnel oxide layer 4, and an interpoly dielectric layer 5. When it is intended to write data into the flash memory unit 1, a threshold voltage of the flash memory unit 1 may be changed by injecting electrons into the charge-trapping layer 2. Accordingly, a digital-level state of the flash memory unit 1 is defined to implement a function of storing data. Here, the process of injecting the electrons to the charge-trapping layer 2 is referred to as a programming process. By contrast, when it is intended to remove the stored data, the injected electrons are removed from the charge-trapping layer 2, and thereby the flash memory unit 1 is restored back to the default state before programming.
However, during the manufacture of the flash memory unit 1, a critical voltage distribution of the flash memory unit 1 may shift due to the variation of the manufacturing process such that the storage state of the flash memory unit 1 cannot be determined correctly, and the foregoing read-disturb phenomenon will happened. In the present flash memory, because the electric field for crossing the tunnel oxide is raised with the microminiaturization of the process of the flash memory, the read-disturb of the flash memory becomes more serious. So that, it drives every manufacturer to develop a mechanism which may ensure that data will be stored correctly.
And, the present mechanism for read-disturb protection is to set an error bit number threshold value during the reading operation, and rewrite the data having the error bits, which is more than the error bit number threshold value, into the other physical erasing unit to ensure the accuracy of the data. However, there are many reasons for occurring error bits. When taking the error bits number as the criterion, it would cause that the rewriting of the flash memory is too often to decrease the life of the rewritable non-volatile memory storage apparatus.
Nothing herein should be construed as an admission of knowledge in the prior art of any portion of the present invention. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention, or that any reference forms a part of the common general knowledge in the art.